1/*
2 * Copyright 2012 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8#include "include/private/SkFloatingPoint.h"
9#include "src/core/SkRasterPipeline.h"
10#include "src/core/SkReadBuffer.h"
11#include "src/core/SkWriteBuffer.h"
12#include "src/shaders/gradients/SkSweepGradient.h"
13
14SkSweepGradient::SkSweepGradient(const SkPoint& center, SkScalar t0, SkScalar t1,
15                                 const Descriptor& desc)
16    : SkGradientShaderBase(desc, SkMatrix::Translate(-center.x(), -center.y()))
17    , fCenter(center)
18    , fTBias(-t0)
19    , fTScale(1 / (t1 - t0))
20{
21    SkASSERT(t0 < t1);
22}
23
24SkShader::GradientType SkSweepGradient::asAGradient(GradientInfo* info) const {
25    if (info) {
26        commonAsAGradient(info);
27        info->fPoint[0] = fCenter;
28    }
29    return kSweep_GradientType;
30}
31
32static std::tuple<SkScalar, SkScalar> angles_from_t_coeff(SkScalar tBias, SkScalar tScale) {
33    return std::make_tuple(-tBias * 360, (sk_ieee_float_divide(1, tScale) - tBias) * 360);
34}
35
36sk_sp<SkFlattenable> SkSweepGradient::CreateProc(SkReadBuffer& buffer) {
37    DescriptorScope desc;
38    if (!desc.unflatten(buffer)) {
39        return nullptr;
40    }
41    const SkPoint center = buffer.readPoint();
42
43    const auto tBias  = buffer.readScalar(),
44               tScale = buffer.readScalar();
45    auto [startAngle, endAngle] = angles_from_t_coeff(tBias, tScale);
46
47    return SkGradientShader::MakeSweep(center.x(), center.y(), desc.fColors,
48                                       std::move(desc.fColorSpace), desc.fPos, desc.fCount,
49                                       desc.fTileMode, startAngle, endAngle,
50                                       desc.fGradFlags, desc.fLocalMatrix);
51}
52
53void SkSweepGradient::flatten(SkWriteBuffer& buffer) const {
54    this->INHERITED::flatten(buffer);
55    buffer.writePoint(fCenter);
56    buffer.writeScalar(fTBias);
57    buffer.writeScalar(fTScale);
58}
59
60void SkSweepGradient::appendGradientStages(SkArenaAlloc* alloc, SkRasterPipeline* p,
61                                           SkRasterPipeline*) const {
62    p->append(SkRasterPipeline::xy_to_unit_angle);
63    p->append_matrix(alloc, SkMatrix::Scale(fTScale, 1) * SkMatrix::Translate(fTBias, 0));
64}
65
66skvm::F32 SkSweepGradient::transformT(skvm::Builder* p, skvm::Uniforms* uniforms,
67                                      skvm::Coord coord, skvm::I32* mask) const {
68    skvm::F32 xabs = abs(coord.x),
69              yabs = abs(coord.y),
70             slope = min(xabs, yabs) / max(xabs, yabs);
71    skvm::F32 s = slope * slope;
72
73    // Use a 7th degree polynomial to approximate atan.
74    // This was generated using sollya.gforge.inria.fr.
75    // A float optimized polynomial was generated using the following command.
76    // P1 = fpminimax((1/(2*Pi))*atan(x),[|1,3,5,7|],[|24...|],[2^(-40),1],relative);
77    skvm::F32 phi = slope * poly(s, -7.0547382347285747528076171875e-3f,
78                                    +2.476101927459239959716796875e-2f,
79                                    -5.185396969318389892578125e-2f,
80                                    +0.15912117063999176025390625f);
81    phi = select(   xabs < yabs, (1/4.0f) - phi, phi);
82    phi = select(coord.x < 0.0f, (1/2.0f) - phi, phi);
83    phi = select(coord.y < 0.0f, (1/1.0f) - phi, phi);
84
85    skvm::F32 t = select(is_NaN(phi), p->splat(0.0f)
86                                    , phi);
87
88    if (fTScale != 1.0f || fTBias != 0.0f) {
89        t = t * p->uniformF(uniforms->pushF(fTScale))
90              + p->uniformF(uniforms->pushF(fTScale*fTBias));
91    }
92    return t;
93}
94
95/////////////////////////////////////////////////////////////////////
96
97#if SK_SUPPORT_GPU
98
99#include "src/gpu/gradients/GrGradientShader.h"
100
101std::unique_ptr<GrFragmentProcessor> SkSweepGradient::asFragmentProcessor(
102        const GrFPArgs& args) const {
103    return GrGradientShader::MakeSweep(*this, args);
104}
105
106#endif
107